[Coco] What do you use for pull-up and pull-down TTL resistor values? (LS series) (coco related project but possibly OT)

[James Ross]

Thanks Dave, between yours and Ed’s answers, I will go w/ using the 4.7k for hard-wiring TTL level inputs high (since that is the value I've seen in numerous locations) and connecting inputs that are low directly to ground. And connect unused inputs (e.g. LS14 chips, etc…) directly to ground as well.  Later I will study the use of using 10k values...  

Hey, that little cyclone II board you sold me is still working great, and I am using it to play around with learning to interface FPGA w/ outside devices. Very slowly, hopefully like the tortoise in "The Tortoise and the Hare"!  Which right now also means learning how shift voltages between 3.3v and 5v … there appears to be several ways of doing that – that will be for a separate question, later!  :)    

James

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From: Coco <coco-bounces at maltedmedia.com> on behalf of Dave Philipsen <dave at davebiz.com>

Generally a 4.7k resistor is used used for pull-up on 5v TTL inputs or open-collector outputs (I have seen values as high as 10k used). A pull-down is not usually needed. It’s good practice to tie any unused input either hi or lo. If you need to tie low just connect directly to ground. No resistor needed.

Dave